Final answer:
William Henry Harrison served only a month in office before dying of pneumonia.
Step-by-step explanation:
The president who only served a month in office before dying of pneumonia was William Henry Harrison. He took office on March 4, 1841, and delivered a lengthy inaugural speech without wearing a coat or hat in cold weather. As a result, he developed pneumonia and died on April 4, 1841.
Learn more about William Henry Harrison's presidency